Self-locking threaded fasteners

ABSTRACT

A self-locking threaded fastener adapted for assembly with a member in which a standard internal thread is formed either by the fastener or a conventional tap. A thread is carried on the shank of the fastener having an included thread angle less than the standard included thread angle, a major diameter greater than is standard for the particular fastener size, and a root width less than is standard. At least one locking lobe is formed on the thread which lobe is engaged by material displaced by the thread whereby to effect locking.

United States Patent Oestereicher 1 Feb.22, 1972 [54] SELF-LOCKINGTHREADED FASTENERS [72] Inventor: Louis OestereichenTeaneck, NJ.

[73] Assignee: Parker-Kalon Corporation, Clifton, NJ.

[22] Filed: May 16, 1969 [211 App]. No.1 825,334

1571 [3.811]. ..l5l/22,t15/46 1715 1m. (it. 39/30 15 11 Heldulfitarch..l51/22;85/46,47,41

[56] References Cited UNITED STATES PATENTS 1,367,168 2/1921 Stanford....151/22 2,278,411 4/1942 Brandel ....151/22 2,581,690 1/1952 Moehleet a1. ....15 l/22 2,679,774 6/1954 MacD0nald.... ....15l/22 3,186,4646/1965 Baumle ....151/22 3,249,142 5/1966 Phipard ....l51/22 3,426,6422/1969 Phipard ..151/22 3,426,820 2/1969 Phipard ..151/22 3,454,0707/1969 Phipard .....151/22 2,352,982 7/1944 Tomalis ..151/22 FOREIGNPATENTS OR APPLlCATlONS 957,675 4/1964 Great Britain ..s5/4e PrimaryExaminerMarion Parsons, Jr. Attorney-W. Bigelow Hall, Richard A. Wiseand Richard B. Mcgley 1571 ABSTRACT A self-locking threaded fasteneradapted for assembly with a member in which a standard internal threadis formed either by the fastener or a conventional tap. A thread iscarried on the shank of the fastener having an included thread angleless than the standard included thread angle, a major diameter greaterthan is standard for the particular fastener size, and a root width lessthan is standard. At least one locking lobe is formed on the threadwhich lobe is engaged by material displaced by the thread whereby toeffect locking.

12 Claims, 6 Drawing Figures illlllu M W PAIENTEDFEB22 1972 In 112 ntorLou/s 0&5 tere/c/zer 5 Z215 Altar/lay SELF-LOCKING THREADED FASTENERSBACKGROUND OF THE INVENTION This invention relates to self-lockingthreaded fasteners and more particularly to such fasteners in which thelocking action is obtained by the combination of a plurality of lobes ona shank portion of the fastener and a unique or nonstandard threadconstruction.

A variety of self-locking threaded fasteners have appeared in the marketplace in recent years. Each of these fasteners have had deficiencieswhich have restricted their universal utilization. Self-lockingfasteners which employ plastic elements to effect locking are expensiveto manufacture and cannot be used in applications involving hightemperature. When special thread formations were used in the past, theresulting self-locking fasteners were again found to have highmanufacturing costs in addition to high installation torque and lowreliability when subjected to vibration.

The features of the invention, together with various novel details ofconstruction, will now be more particularly described with reference tothe accompanying drawings and pointed out in the claims. It is to beunderstood that the particular embodiments of the invention shown in thedrawings are for illustration purposes only and are not to be construedas a limitation of the invention. It is also to be clearly understoodthat the features of this invention may be used on any threaded fastenerincluding bolts as well as screws.

DRAWING DESCRIPTION FIG. 1 is a side elevation of a metal screwembodying features of this invention;

FIG. 2 is a view similar to FIG. 1 ofa metal screw illustrating analternate embodiment of this invention;

FIG. 3 is an enlarged fragmentary longitudinal sectional view takenapproximately along lines III-III of FIG. 1;

FIG. 4 is a fragmentary perspective view, on an enlarged scale,illustrating the relationship of the threads on the shank portion of thescrew shown in FIG. 1 with standard internal threads in a member intowhich said screw is inserted;

FIG. 5 is a fragmentary plan view on an enlarged scale of one of thethread sections shown in FIG. 4; and

FIG. 6 is a sectional view, on an enlarged scale, illustrating theswaging action of the threaded shank portion of the screw illustrated inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of ascrew 10 illustrating the invention is shown in FIG. 1. The screw 10 hasa forward, tapered pilot end A and a shank B. The locus of thisinvention resides in the construction of the threaded shank portion B ofthe screw 10 per se and in the use of this construction in combinationwith a pilot end A as shown and to be described. The pilot end A has aplurality of thread-swaging lobes for swaging or tapping a standardinternal thread in a member into which the screw 10 is to be inserted.The pilot end A is shown and described primarily to facilitate acomplete description of the utility and broad usage of the presentinvention. It is to be clearly understood, however, that the novelfeatures of this invention are not limited to use on a screw having apilot end such as shown in FIG. 1. On the contrary, the pilot end A maybe eliminated and a conventional tapping tool such as described in U.S.Pat. No. 2,991,49l, issued July I], 1969, in the name of D. P. Welles,Jr., may be used to form a standard internal thread in a member intowhich a screw embodying the present invention is to be inserted. Theswaging lobes 20 of the pilot end A may be of a construction such asdescribed in U.S. Pat. No. 3,426,642, issued Feb. 11, 1969 in the nameof H. F. Phipard, Jr. or of any other convenient construction capable oftapping a hole.

Conventional or standard threads have an included thread angle of 60.The rearmost thread 21 on the pilot end A of the screw 10 has anincluded thread angle C of 60 and therefore will swage an internalthread having a standard included mac:

thread angle. Further, the other dimensions of the rearmost thread 21 onthe pilot end A are such that a standard internal thread will be formedthereby. A standard internal thread such as would be swaged by the pilotA or formed by conventional tapping tools is shown in FIG. 6 andidentified by the reference character 30. A fuller appreciation of thefunction or effect of the lobes 20 on the pilot end may be obtained byreference to the above-cited U.S. Pat. No. 3,426,642.

The threads on the shank portion B have an included thread angle D, inthe preferred embodiment, of approximately 35 to 55. The major oroutside diameter of the threaded shank is 5 to 15 percent greater thanthe major diameter of the standard thread conventionally used for agiven screw size. Thus, the outside or major diameter of the thread 41,for example, is 5 to 15 percent greater than the outside or majordiameter of the thread 21. Further, as clearly illustrated in FIGS. Iand 6, the width of the threads at the root (W in the shank portion B issmaller than the root width of a standard thread W Compare W and W inFIG. 6. Thus, when the threaded shank portion B is inserted into aconventionally tapped hole such as would be swaged by the pilot end A,the threads on the shank portion B swage a deeper and sharper or morepointed internal thread than was formed by the pilot end or tap. Thatis, the outer portion of the shank threads swage a slightly moreelongated or enlarged internal thread. The result is that material isswaged or forced toward the root of the thread. The relative size andshape of the thread on the shank portion B compared to those of astandard internal thread are such that little appreciable increase inrequired driving torque results.

In the illustrated preferred embodiment, the threaded shank portion Balso has a root diameter 5 to 15 percent greater than the root diameterof the standard thread conventionally used for a given screw size. Thus,metal is forced from the crest of the standard internal thread outwardlyalong and into engagement with the flanks of the threads on the shankportion B. Again, due to the small magnitude of the size differential,no appreciable increase in required driving torque results.

A comparison of the thread form on the shank portion B with aconventional thread may be obtained by comparing the thread outline 32which is that formed by the shank portion B with a standard threadoutline 30, see FIG. 6.

A plurality of locking lobes 44 are formed at spaced locations on thethreaded shank portion B. The locking lobes 44 are disposed in a spiralpattern on the shank portion B in the preferred embodiment asillustrated in FIG. I. The specific angle of the spiral may be variedfor various diameters and lengths of screws. The locking lobes 44 aredisposed in a straight line in the alternate embodiment shown in FIG. 2.The number and disposition of lobes is determined by the requirements ofthe particular application.

As best shown in FIGS. 4 and 5, the locking lobes are preferably of asubstantially triangular configuration. That is, the crest 46 of each ofthe locking lobes 44 is relatively elongated and the edges 48, 50 of thelobes on the thread flank converge from a maximum spacing at the crestof the thread to a minimum spacing at the root of the thread. Theleading end of the crest of the lobe 44, in the preferred embodiment,rises outwardly from the crest of the associated thread and the trailingend of the lobe crest falls back into the associated thread in asubstantially arcuate configuration. The essentially triangular portionof the lobe on the flank of the associated thread is preferably ofbulbous configuration in transverse cross section taken along the threadflank. As will be discussed, this preferred locking lobe configurationfacilitates the flow of swaged metal into locking position relative tothe locking lobe 44 when the shank portion B is inserted.

When the shank portion B is inserted into a member having a standard,appropriately sized, internal thread, the outer portion or sharp crestof the shank threads, e.g., 41, will swage metal downwardly along theflanks of the thread. The displaced metal will also be curved around thelocking lobes whereby the lobes become surrounded by displaced material.The screw will thus become locked in position upon complernum tion ofthe insertion operation. The arcuate lobe crest 46 penetrates or swagesadditional material into locking position.

The essentially triangular configuration of the locking lobes 44facilitates the flow of displaced metal from the crest of the threadalong the edges 48, 50 of the lobe. That is, this particularconfiguration provides a minimum resistance to the flow of displacedmetal into a locking relationship with respect to the locking lobes.Displaced metal is urged into blocking or locking position along theedge 50 of the lobe as a result of the taper thereof. However, thisconfiguration does not result in excessive binding or build up ofmaterial at the root area and thereby avoids the increase in drivingtorque which would result if this occurred.

In the preferred embodiment, metal is also urged into locking positionrelative to the locking lobes 44 as a result of the oversized rootdiameter of the threaded shank portion B. A properly designed or sizedshank thread will result in the locking lobes 44 being completelysurrounded by displaced metal. Additionally, proper design or sizingwill result in essentially complete engagement of the flanks of thethreads on the shank portion B with the reformed internal thread.

Thus, applicant has provided a locking thread capable of securelylocking a screw or bolt in a fixed position. An extremely highresistance to vibration is also attained. As noted above, theconstruction is applicable to any threaded fastener. lf preferred, thesize of the internal thread formed by the pilot end A may be less thanthe standard thread size to effect additional material displaced by thethread shank portion B. The particular included thread angle, majordiameter, width of the thread at the root, and root diameter of thethread shank portion B may be varied depending on the desired drivingtorque and resistance to removal. Also, the number, size and shape ofthe locking lobes may be varied depending on the amount of lockingaction desired.

Having thus described a preferred embodiment of my invention, what Iclaim as new and desire to secure by Letters Patent of the United Statesis:

1. A self-locking threaded fastener adapted for assembly with a memberin which a standard internal thread is formed comprising a shank ofsubstantially circular cross section hav ing a circular helical threadcarried thereon, said helical thread having a root, flanks, and a crestdefining an included thread angle less than the standard included threadangle and having a major diameter substantially constant and greaterthan the standard major diameter for the particular fastener size, andat least one locking lobe superimposed on said thread extending alongedges outwardly beyond said flanks and having a lobe crest extendingbeyond the major diameter of said thread, said edges of said lobeconverging from a maximum spacing at said lobe crest toward the root ofsaid thread whereby material displaced by said thread during insertionof said fastener into the internally threaded member is urged intolocking engagement with said locking lobe.

2. A self-locking threaded fastener according to claim 1 wherein theincluded thread angle of the thread carried by the shank is to 55.

3. A self-locking threaded fastener according to claim 1 wherein themajor diameter of the thread carried by the shank is 5 to 15 percentgreater than the standard major diameter for the particular fastenersize.

4. A self-locking threaded fastener according to claim 1 wherein theroot width of the thread carried by the shank is less than the standardroot width for the particular fastener size.

5. A self-locking threaded fastener according to claim 4 wherein theincluded thread angle of the thread carried by the shank isapproximately 35 to 55 degrees and the major diameter thereof is 5 to 15percent greater than the standard major diameter for the particularfastener size.

6. A self-locking threaded fastener according to claim I wherein saidlocking lobe has a substantially bulbous transverse cross section on theflanks of the thread.

7. A self-locking threaded fastener according to claim 6 wherein saidlocking lobe is of essentially triangular configuration on the flanks ofthe thread having a maximum width at the crest of the thread and thesides thereof converging to a minimum spacing substantially at the rootof the thread.

8. A self-locking thread-forming fastener having a substantiallycylindrical shank portion and a tapered pilot end, said tapered pilotend having a helical thread carried thereon and a plurality ofcircumferentially spaced discrete thread-forming lobes expressed fromthe flanks of saidipilot end thread, the thread-forming lobe nearestsaid shank portion having a configuration adapted to swage asubstantially standard internal thread in a generally cylindricalsurface, said substantially cylindrical shank portion having asubstantially circular helical thread carried thereon, said shank threadhaving a root, flanks, and a crest, defining an included thread angleless than the standard included thread angle and having a major diametersubstantially constant and greater than the standard major diameter forthe particular fastener size, and at least one locking lobe superimposedon said shank thread extending along edges outwardly beyond said flanksand having a lobe crest extending beyond the major diameter of saidthread, said edges of said lobe converging from a maximum spacing atsaid lobe crest toward the root of said thread whereby materialdisplaced by said shank thread during insertion of said fastener isurged into locking engagement with said locking lobe.

9. A self-locking thread-forming fastener according to claim 8 whereinthe root width of the thread carried by the shank portion is less thanthe standard root width for the particular fastener size.

10. A self-locking thread-forming fastener according to claim 8 whereinthe included thread angle of the thread carried by the shank portion isapproximately 35 to 55 and the major diameter thereof is 5 to 15 percentgreater than the standard major diameter for the particular fastenersize.

11. A self-locking thread-forming fastener according to claim 8 whereinsaid locking lobe has a substantially bulbous transverse cross sectionon the flanks of the shank thread.

12. A self-locking thread-forming fastener according to claim 8 whereinsaid locking lobe is of essentially triangular configuration on theflanks of the shank thread having a maximum width at the crest of theshank thread and the sides thereof converging to a minimum spacingsubstantially at the root of the shank thread.

1. A self-locking threaded fastener adapted for assembly with a memberin which a standard internal thread is formed comprising a shank ofsubstantially circular cross section having a circular helical threadcarried thereon, said helical thread having a root, flanks, and a crestdefining an included thread angle less than the standard included threadangle and having a major diameter substantially constant and greaterthan the standard major diameter for the particular fastener size, andat least one locking lobe superimposed on said thread extending alongedges outwardly beyond said flanks and having a lobe crest extendingbeyond the major diameter of said thread, said edges of said lobeconverging from a maximum spacing at said lobe crest toward the root ofsaid thread whereby material displaced by said thread during insertionof said fastener into the internally threaded member is urged intolocking engagement with said locking lobe.
 2. A self-locking threadedfastener according to claim 1 wherein the included thread angle of thethread carried by the shank is 35* to 55*.
 3. A self-locking threadedfastener according to claim 1 wherein the major diameter of the threadcarried by the shank is 5 to 15 percent greater than the standard majordiameter for the particular fastener size.
 4. A self-locking threadedfastener according to claim 1 wherein the root width of the threadcarried by the shank is less than the standard root width for theparticular fastener size.
 5. A self-locking threaded fastener accordingto claim 4 wherein the included thread angle of the thread carried bythe shank is approximately 35 to 55 degrees and the major diameterthereof is 5 to 15 percent greater than the standard major diameter forthe particular fastener size.
 6. A self-locking threaded fasteneraccording to claim 1 wherein said locking lobe has a substantiallybulbous transverse cross section on the flanks of the thread.
 7. Aself-locking threaded fastener according to claim 6 wherein said lockinglobe is of essentially triangular configuration on the flanks of thethread having a maximum width at the crest of the thread and the sidesthereof converging to a minimum spacing substantially at the root of thethread.
 8. A self-locking thread-forming fastener having a substantiallycylindrical shank portion and a tapered pilot end, said tapered pilotend having a helical thread carried thereon and a plurality ofcircumferentially spaced discrete thread-forming lobes expressed fromthe flanks of said pilot end thread, the thread-forming lobe nearestsaid shank portion having a configuration adapted to swage asubstantially standard internal thread in a generally cylindricalsurface, said substantially cylindrical shank portion having asubstantially circular helical thread carried thereon, said shank threadhaving a root, flanks, and a crest, defining an included thread angleless than the standard included thread angle and having a major diametersubstantially constant and greater than the standard major diameter forthe particular fastener size, and at least one locking lobe superimposedon said shank thread extending along edges outwardly beyond said flanksand having a lobe crest extending beyond the major diameter of saidthread, said edges of said lobe converging from a maximum spacing atsaid lobe crest toward the root of said thread whereby materialdisplaced by said shank thread during insertion of said fastener isurged into locking engagement with said locking lobe.
 9. A self-lockingthread-forming fastener according to claim 8 wherein the root width ofthe thread carried by the shank portion is less than the standard rootwidth for the particular fastener size.
 10. A self-lockingthread-forming fastener according to claim 8 wherein the included threadangle of the thread carried by the shAnk portion is approximately 35* to55* and the major diameter thereof is 5 to 15 percent greater than thestandard major diameter for the particular fastener size.
 11. Aself-locking thread-forming fastener according to claim 8 wherein saidlocking lobe has a substantially bulbous transverse cross section on theflanks of the shank thread.
 12. A self-locking thread-forming fasteneraccording to claim 8 wherein said locking lobe is of essentiallytriangular configuration on the flanks of the shank thread having amaximum width at the crest of the shank thread and the sides thereofconverging to a minimum spacing substantially at the root of the shankthread.